This invention relates to the shaping of glass sheets by roll forming. As described in U.S. Pat. No. 3,701,644 to Robert G. Frank, the roll forming method comprises conveying a succession of glass sheets through a furnace where each sheet in turn is heat softened and without stopping the sheets, momentarily engaging the opposite surfaces of each heat softened glass sheet between opposite sets of rotating forming rolls of complementary shapes as each sheet moves continuously through the roll forming station. Each sheet is disengaged after pressurized engagement for sufficient time to shape the sheet and while the sheet continues to move into a cooling station, where the glass is cooled sufficiently rapidly to impart at least a partial temper thereto.
In the various embodiments of the roll forming apparatus disclosed in the aforesaid patent, glass sheets are engaged between rotating segmented forming rolls that comprise an upper set of rotating forming rolls of convex outer configuration in the axial direction of the upper forming rolls and a lower set of rotating forming rolls having a concave outer configuration along the axis of the lower forming rolls that is complementary to the convex outer configuration of the upper rolls. The lower set of forming rolls move upward from a recessed position below a plane of support defined by spaced, rigidly supported, rotating conveyor rolls into a glass sheet engaging position wherein the bottom set of rotating forming rolls engages the glass, first at its side edge portions and then gradually increases the area of engagement inwardly toward the longitudinal center line of the glass as it lifts the latter completely above the rigidly supported conveyor rolls. Because of this initial engagement between the rising rotating forming rolls and the longitudinally extending side edge of the glass sheets, the glass sheets tend to kink along one or both side edges, depending upon the temperature pattern in the furnace in which the glass sheets are heated to a heat softened condition to enable them to be shaped by engagement between opposed sets of shaped rotating forming rolls.
U.S. Pat. No. 3,676,098 to Hall relates to press bending heat softened glass sheets and controls and retains the final bent shape of the sheets by positively cooling flat heated sheets over their entire area between the time they leave a furnace and the time they arrive at a glass shaping station. The Hall patent finds it necessary to positively cool the entire surface of the glass sheet.
U.S. Pat. No. 3,396,000 to Carson, Ferguson, Ritter and Hymore discloses the application of air blasts to the upper surface only adjacent to the opposite longitudinal side edges of glass sheets between a furnace exit and a cooling station in order to impart a bend along restricted areas of the opposite longitudinal side edges of the glass sheet.